1. Technical Field
The present invention relates to a radio transmitting apparatus and radio transmission method for performing uplink band allocation through scheduling.
2. Description of the Related Art
The technical specification group radio access network (“TSG RAN”) of the 3rd generation partnership project (“3GPP”) is currently conducting studies on a next-generation mobile communication system, referred to as long term evolution (“LTE”). Working group 1 of the TSG RAN (“RAN 1”) is moving forward with the standardization of LTE radio access schemes. Of these, single-carrier FDMA (“SC-FDMA”) is adopted as the uplink radio access scheme for LTE.
This SC-FDMA is has a characteristic of low PAPR (Peak to Average Power Ratio), and is suitable to the uplink where transmission power of a terminal is limited. Therefore, to transmit control information of layer 1 (“L1”) or layer 2 (“L2”) at the timing user data is transmitted while maintaining the low PAPR characteristic of SC-FDMA, studies are underway to multiplex the control information, user data and reference signal (pilot for channel estimation) in the time domain, by the terminal.
As L1/L2 control information transmitted on the uplink, for example, downlink ACK/NACK and downlink CQI (Channel Quality Indicator) are generated independently of uplink user data transmission and depending on the presence/absence of user data transmission on the downlink. Therefore, the number and combinations of L1/L2 control information that is time-multiplexed with uplink data vary, and therefore Non-Patent Document 1 describes a study on a method for dynamically allocating symbols of control information and user data according to the L1/L2 control information to be actually time-multiplexed (hereinafter “dynamic symbol allocation”), thereby maximizing uplink frequency utilization efficiency. That is, the number of symbols of L1/L2 control information and the number of symbols allocated to user data are changed according to the content of the L1/L2 control information to be actually time-multiplexed.
Furthermore, with LTE, studies are underway to adopt adaptive scheduling in accordance with channel quality in the uplink (i.e., adaptive modulation and time-frequency scheduling according to channel conditions).
When the number of symbols allocated to user data varies depending on the presence/absence and combinations of L1/L2 control information that are time multiplexed as described in above Non-Patent Document 1, if uplink band allocation is performed through adaptive scheduling, a base station (hereinafter “BS”) needs to report uplink band allocation information that is required upon transmitting data on the uplink, to a mobile station (hereinafter “MS”), which results in an increase in the amount of this information.
When the BS performs adaptive scheduling on the uplink according to channel conditions, the BS measures uplink channel quality using the reference signals transmitted from each MS and determines the bandwidth to allocate to each MS, the number of symbols (or the number of subframes formed with a plurality of symbols), and transmission parameters (including the M-ary modulation value, the coding rate of error correcting code, the spreading factor, etc.) based on the band requirement information for each MS, or, more specifically, based on the amount of data to be transmitted, transmission data rate, QoS (Quality of Service) information and so on. The BS reports the determined information (i.e., band allocation information) to each MS using a downlink control channel.
Furthermore, in the band allocation for E-DCH described in Non-Patent Document 2 and Non-Patent Document 3, a BS reports to a MS only the time slots allocated to the MS and the upper limit of transmission power, and the MS selects the coding rate, spreading factor and the number of bits of transmission data of the allocated time slots within the range of allowed transmission power, and reports the selected transmission parameters using the TB indexes (see FIG. 1) provided on a per transport block size basis (hereinafter “TB size”), so that the BS performs receiving processing.
TB size shows the number of transmission data bits before the CRC (Cyclic Redundancy Check) bits are added, and is derived from a combination of available transmission parameters. One TB size id associated with one coding rate and spreading factor. The M-ary modulation value is fixed and needs not be reported, so that, by reporting the TB size, the receiving side is able to acquire the number of information bits, the spreading factor and the coding rate.
Even when a centralized control system is assumed in which the BS determines the coding rate, spreading factor and the number of bits of transmission data, the BS is still able to control band allocation by including the TB size in band allocation information.    Non-Patent Document 1: R1-060111, Ericsson, “Uplink Control Signaling for E-UTRA,” 3GPP TSG RAN1 WG1 Meeting #44, Denver, USA, Feb. 13-17, 2006    Non-Patent Document 2: 3GPP TS 25.321V6.7.0 (Annex)    Non-Patent Document 3: 3GPP TS 25.212V6.7.0 (4.3 Transport format detection)